Custom MadeElectronic OilPressure Gauge

Custom MadeElectronic OilPressure Gauge

44 GEARS May/June 2005

Acouple of months ago, ProjectPage showed you how to makean electronic oil pressure gaugefrom a discarded Dodge 42/46RE gover-nor transducer. There were so manycomments about it I decided to do itagain. But this time, we are going to usea transducer from a 45RFE transmission.The reason well use the 45RFE trans-ducer is that this one can read up to 200psi. The 42/46RE transducer only has arange of zero to about 100 psi. Just think,with these two custom sensors, youll beable to check almost any transmissionout there. Ill bet with the money yousave, you could afford to buy an oscillo-scope, or a second scan tool or anexhaust gas analyzer. Okay, Im justdreaming.

There are lots of advantages of anelectronic pressure gauge. I always feelmore secure with an electric transducerattached to a car during a test drive.Also, they are easier to install. The wirecable is simpler to route around theengine compartment than a high pres-sure hose. And, a wire cant burst andthrow oil all over the place. That hap-pened once. Ill never forget what amess that was. So lets get started.

The first thing you need is an old45RFE pressure transducer. Next youllneed is to adapt the sensor so you canthread it into the pressure taps on thevarious transmissions. Youll also needa 5-volt power source and a voltmeter.The voltmeter is used to display thevoltage change from the transducer.Since the voltmeter displays pressure asvoltage, you need to refer to the voltage

vs. pressurechart at the endof this article.But first, letsadapter yourtransducer andmake the powersource.

I found ar e a d y - m a d eadapter fromMiller SpecialTools. Its basi-cally a block of metal, which allows thetransducer to mount on one end and hasa short hose to allow you to test theaccuracy of the transducer on the45RFE. There is also a 1/8" pipe threadhole to fit a gauge on the other end.(For about $100.00, Miller will ship itto you). I decided to be more creativeand look for an alternate solution.

I looked around the shop andfound a discarded extension housingfrom an E4OD. I chose it for the fol-lowing reasons. The bolt holes were.427" which is only .002" larger thanthe hole in the case where the 45RFEtransducer mounts. I then decided that acouple of the holes were deep enoughfor the depth of the sensor and to tap theother end to allow me to thread a pipefitting into. I finally decided on remov-ing the upper mounting area because ithad enough metal off to the side to drilland tap a screw to mount the transduc-er to it just like it was mounted on thecase (figure 1).

After cutting off the piece, I drilledand tapped a hole for a 1/4-20" screw to

mount the transducer. The easy partwas done. In order to install the 1/8"pipe fitting, I realized I would need alarger adapter to thread into the mountfirst. It looked simple to first run somethreads into the mount and fit a 1/4" to1/8" pipe reducer. After drilling theother end with a 7/16" bit, I didnt likehow little metal was left between theopening and the pressure end of thetransducer. I decided that I needed anadapter with a deeper hole to tap into.Otherwise I would be cutting threadsinto the bore where I had mounted thetransducer. WHAT NOW.

Since this was just an experimentanyway, I shortened the transducer bycutting off one o-ring (figure 2). After

by Dave SkoraPROJECT PAGE

Figure 1: Adapting an E4OD Extension Housing

Use The SmallPiece Here

Figure 2: Shortening The Transducer

projectpag5-05.qxd 4/18/05 2:17 PM Page 44

T: 419.499.2502 F: 419.499.3337www.TransTec.com Milan, OH 44846

1. Better PartsNobody makes transmission parts moredependable. Cortecos Technology Centerhouses 70 engineering and materials pro-fessionals that have developed hundredsof patents and proprietary compounds that

improve gasket and seal performance. Our globally integratedsupply of products from 85 auto-motive operations in 27 countriesinsures that we produce the bestgaskets and seals.

2. More Parts.We offer more parts and sell more parts than any other kit supplier.

Every 12.7 seconds someone, somewhere,rebuilds a transmission with a TransTec kit.Thats 24 hours a day, 7 days a week, 365 days ayear... and that doesnt even include our O.E.service kits.

3. History of Satisfied CustomersThe companies that formed to bring you TransTec kits have along history of serving satisfied customers. In fact,weve been an O.E. supplier as long as therehave been cars!

4. Lowest Overall CostAdd it all up and youll find TransTeckits have the lowest overall cost.Better parts and better performancemeans less chance of a comeback. Getit all with TransTec transmission kitsfrom Corteco, the O.E. supplier withaftermarket vision.

Our Kits.1. Price

Their Kits.

Its a tough decision.Take your time.

transtec-corteco placed4-05.qxd 3/14/05 10:27 AM Page 9

tapping the hole, I installed the adapterand 1/8" pipe to the mount. My 45RFEtransducer pressure adapter was done(figure 3). If you have access to amachine shop, you could create a muchbetter adapter than mine. Next, youllneed the following electrical parts.

A 45RFE pressure transducerA transducer connectorA cigarette adapter (Includes inline

fuse)A 5-volt IC regulator2 capacitors10-15 ft. length of 22-30 gauge

stranded wireHeat-shrink tubingAn inline 1 amp fuse 1/4-1/8" pipe adapterLength of 1/8" pipe

By following the included wiringschematic (figure 4), you should wireyour IC regulator, capacitors and inlinefuse to the cigarette adapter. Also add atest lead from the ground point for yournegative voltmeter lead.

There is one more challenge youneed to deal with if you want to makethis transducer work. The problem isthe connector. As far as I can tell, theconnector is part of the main transmis-sion harness and not available separate-

ly. I made my own connector with 3terminals from an old 46RE connector.I then sprayed PAM around the trans-ducer terminals and filled the cavitywith Silicone. When dried, I couldremove and install the 3 connectors. Itfeels a little rubbery, but it works.Another way it could be done, is tomake the terminals permanent on thetransducer and use your own male-female electrical connector to plug ittogether. After you figured what worksbest for your connector, wire the trans-ducer connector to the other end of thestranded wires.

If you use an actual connector,match up the colors with the followingchart or use the connector view tolocate where each wire belongs. Makesure your 5-volt source and groundleads are connected to the right termi-nals. The third lead for the signal out ofthe transducer (figure 5). The other endbecomes the positive test point for yourvoltmeter.

Connect your cigarette adapter to avehicle. Attach your modified 45RFEtransducer to a pressure tap and connectthe wiring harness. Using the DC scaleof your voltmeter, connect your meterto the test points. Use the chart to con-

vert your voltmeter reading to the cor-rect psi value. Remember, this trans-ducer has a range of zero to around200psi.

When I checked mine, it followedthe expected pressure and voltage val-ues. I also raised the pressure to 300psito see if the transducer would fail. Itdidnt. The transducer still followed theexpected values. So, now we know youcan get a reliable electronic pressuregauge from a few old parts and yourvoltmeter. If you want to, you couldmake several pressure sensors.Remember, that this sensor is accuratebetween 40-200psi. If you want anaccurate gauge with a 0-100psi range,use the 42/46RE governor transducer.Happy gauging.

46 GEARS May/June 2005

Figure 3: Finished Adapter withTransducer

Black / Red(ground)

Custom Made Electronic Oil Pressure Gauge

Gray / Light Blue

(5-Volts)

Figure 5: Line Pressure Sensor (4.7L)

Purple / Tan (sensor signal)

VOLTAGE vs. PRESSURE ACTUAL METER READING45RFE Pressure Transducer

psi..DC Voltage psi..DC Volts0....0.8 0 ..........................0.7920..1.2 20..........................1.2140..1.6 40..........................1.6360..2.0 60..........................2.0180..2.4 80..........................2.42100....3.0 100........................2.79120....3.2 120........................3.191403.6 140........................3.611604.0 160........................3.991804.4 180........................4.382004.8 200........................4.82

12vInput Output

5v

LF

Gnd

from fusedvehicle power

CapacitorRadio Shackpart number272-135

CapacitorRadio Shackpart number272-135

Radio Shack part number276-1770

0.1 F 0.1 F

5 VOLT REGULATOR

Transmission Governor Pressure SensorConnector Terminal Identification

Terminal Wire Color Function

1......................Red............ 5-Volt Supply2 ....................White ........ Sensor Signal3 ....................Black ...... Sensor Ground

Figure 4

projectpag5-05.qxd 4/18/05 2:17 PM Page 46

accurate1104.qxd 11/2/04 3:07 PM Page 11